1. Field of the Invention
The present invention relates to a method for reducing sulfur compounds in hydrocarbon streams.
2. Related Art
There is a vast body of art relating to the removal of sulfur compounds from hydrocarbon streams, such as the removal of sulfur compounds from oil fractions and heavy residue. Generally these procedures relate to hydrotreating the fraction at elevated temperatures and pressures usually in the presence of a solid contact material, e.g., U.S. Pat. Nos. 4,447,314; 4,411,771; 4,212,729; 3,983,030; 3,898,155; 3,876,530 and 3,674,680. These procedures are costly because of equipment requirements and catalyst as well as the requirement for relatively frequent regeneration of the catalyst.
The present invention is directed to the removal of small amounts of sulfur compounds from hydrocarbon streams to extremely low levels. The treated streams of the present invention may be final product streams or may be intended for subsequent processing where sulfur is detrimental.
The reactivity of organic sulfur compounds with various other materials has been observed. For example, sodium hypochlorite has been observed to oxidize some organic sulfur compounds, e.g., Homer, et al., "Sur Oxidation Von Thioethers mit Hypochlorit", Phosphorus Sulfur, 22 (1) p. 5-11 (1985), documents oxidation studies of thioethers in toluene with dilute aqueous sodium hypochlorite under a variety of pH values and hypochlorite concentrations. Other art shows MeSH, Me.sub.2 S and Me.sub.2 S.sub.2 were removed by oxidation with NaOCl (5 ppm each) in two stages of scrubbing, at pH 7 and 11, [CA 92 202700p (1980) "Oxidative Treatment of Sulfur Compounds with Sodium Hypochlorite" Abe, et al., Anzen Kogku 1979, 18(5), 271-4]; odorous compounds were removed from Kraft Paper mill waste gases by scrubbing with an aqueous solution containing hypochlorite (5.5% NaOCl and 45% Na.sub.2 CO.sub.3 pH 11.3), [CA 92 81619L (1980) "Method and Apparatus for Removing Reduced Sulfur Compounds from Vapors and/or Gas Streams" Parahacs, et al., Can 1062440 18 Sept. 1979]; waste gases from an edible oil plant were deodorized (MeSH, Me.sub.2 S and H.sub.2 S removed) with 500-1000 mg NaOCl/L solution [CA 102 190256h "Treatment of Waste Gas", Japan Kakai Tokyo, JP No. 6,007,024 (8,507,924) Jan. 16, 1985]; comparative studies showed NaOCl was the most practical scrubbing agent for reducing S emissions in flue gas in paper mills [CA 89 168128j "Removal of Organic Sulfur Compounds from Kraft Emissions Using Wet Scrubbing Techniques" Azarnionch, et al., Prepr Pap Annual Meeting Tech Sect CPPA, 63rd, 1977 A 179-84]; MeSH and Me.sub.2 S were treated with circulating aqueous Ca(OCl).sub.2 for complete removal [CA 91 93636d "Removal of Gaseous Organic Sulfur Substances" Muraoka, et al., Jpn Tokyo Koho No. 7,904,699, Mar. 9, 1979]; and a turbulent, 3-stage contact absorber removed organic S compounds from flue gas with 500-700 ppm NaOCl at a pH of 9-9.5 [CA 88 141056b "Novel Wet Scrubbing Techniques for the Removal of Hydrogen Sulfide and Organic Sulfur Compounds," Prahacs, et al., Proc Int Clean Air Cong 4th 1977; 752-S].
Another example of the reactivity of organic sulfur compounds is the reactivity of carbon disulfide with base forms of anion exchange resins which is known from work relating to detoxification of waste water, removal of acid gases from waste gases and formation of useful polydithiocarbonates heavy metal removal catalyst e.g., Chemical Abstracts 90, 15742a; 87, 118723n; 87, 11197h; 88, 94130j; 79, 78527v; 79, 147114e; 79, 107945v and 80, 121773q. The NaOCl treatment and contact with anion exchange resin are totally different processes. The former converts low boiling sulfides to high boiling materials and the latter extracts the CS.sub.2 from the stream.
With the removal of tetraethyl lead from gasoline, straight run gasoline, which has poor BVON characteristics will not be suitable for blending into gasoline. However, by separating isoalkanes from the n-alkanes the n-alkanes can be isomerized to isoalkanes, and a good blending value material is recoverable. There is usually a small amount of sulfur in various forms present. The preferred low temperature isomerization catalysts are sulfur intolerant (1 ppm or less sulfur in feed). Hence removal of the sulfur (including CS.sub.2) in a simple fashion is necessary to achieve a useful catalyst life.
It is an advantage of the present invention that small amounts of organic sulfur compounds may be substantially removed from hydrocarbon streams. It is a feature of the present invention that a process for such treatment is provided using very moderate treatment conditions. These and other advantages and features will become apparent from the following description.